The work described in this proposal is directed at the development and elaboration of the nuclear magnetic resonance (nmr) method Chemically Induced Dynamic Nuclear Polarization (CIDNP) and its application to a range of biophysical problems. Photo-CIDNP is the observation of greatly enhanced signal intensities in the nmr spectrum of the diamagnetic products of radical pair reactions. This effect is observed when photo-excited dye molecules reversibly attack accessible surface residues on proteins and in nucleic acid, and is therefore an excellent method for studying interactions among biological molecules. Three specific areas of applications are proposed. (1) Peptide fragments corresponding to the exon sequences of Beta-globin can be isolated and their re-assembly studied by photo-CIDNP. This is a direct approach to understanding the nature of functional domains in proteins, and the particular effects of local protein structure on the electronic properties of heme. (2) We have shown that photo-CIDNP can be observed for membrane proteins, offering the opportunity to determine the surface topology and orientation of membrane proteins. Four peptides have been selected for study: gramicidin, a peptide antibiotic which forms transmembrane ion channels; mellitin, the major peptide component of bee venom; M-13 coat protein, the major coat protein of the nonlytic coliphage M-13, and Beta-endorphin, the C-terminal fragment of Beta-lipotropin possessing extraordinary analgesic action. In each case, information will be otained on the manner in which the protein is oriented in the lipid bilayer. (3) Photo-CIDNP can be detected for guanosine bases in single-stranded regions of oligonucleotides. Several model systems are proposed to assess the mechanism and versatility of using guanosine CIDNP to study nucleic acid structure. Several carefully chosen tRNAs will be studied to determine the accessibility of guanosine residues in different single-stranded regions of tRNAs. These investigations form the basis for possible studies of tRNA-protein inter-actions by the photo-CIDNP technique.